Specific solvent effects on the structure and reaction dynamics of benzophenone ketyl radical

Complex formation reaction between benzophenone ketyl (BPK) radical and tri ethylarnine was investigated by means of transient absorption and time-reso lved ESR methods. The formation constants (K-f's) in benzene, toluene, o-xy lene, and anisole were measured by a transient absorption method. The entha lpy and entropy changes upon the complex formation were determined by van't Hoff plots of K-f values around 300 K. The DeltaG values in the complex fo rmation reaction at 298 K were calculated from these thermodynamic paramete rs, which show notable difference from those in aliphatic solvents and chlo rotoluenes previously reported. The BPK conformation in these solvents was investigated by analyzing the time-resolved ESR spectra of BPK and by the D FT calculation. The hyperfine coupling constant of hydroxy-proton (a(OH)) w as found to depend on solvent as well and there exists a clear correlation between the a(OH) and K-f (or DeltaG) values. It was concluded that the con formation of BPK, especially the conformation between OH and two phenyl gro ups, depends on the solvation and is an important factor to control the com plex formation reaction.